This invention relates generally to a method and apparatus for use in connection with the maintenance of paper machines and, more particularly, to a method and apparatus for introducing a closed fabric loop over associated rolls in the paper machine.
It is understood that in the following description, the term "fabric" is used in its most general sense to designate the various materials employed to form the endless loops in the various paper machine sections, i.e., the drying, pressing and forming sections of the paper machine. Thus, the fabric may comprise a felt used in the drying and pressing sections of the machine or wire utilized in the single or twin-wire sections of paper machines.
Various systems for changing the fabrics in paper machines are presently known. For example, seamed fabrics, such as the felt used in paper machine drying sections, are usually changed without any problem by loosening and then separating the seam of the old felt whereupon the new felt is attached with the paper machine running at a relatively slow speed whereupon the new felt is threaded through the drying section. The old felt may then be removed and the new felt seamed to form the fabric loop and appropriate tensioning operations accomplished.
Another conventional technique for changing an endless drying felt comprises unfastening the bearings on the service side of the paper machine whereupon the new felt is urged over the rolls in the axial direction relative thereto.
A conventional technique for changing the press felts in a paper machine comprises detaching the ends of the rolls located within the felt loop together with their bearing means from the machine frame on the service side of the paper machine and removing them entirely therefrom. The press sections in large paper machines are commonly provided with associated lifting apparatus whereby these rolls can be raised and supported during the felt change operation without the necessity of additional lifting equipment. Such lifting apparatus usually comprise hoists which are either directly suspended from the frame of the paper machine or, alternatively, comprise upright cranes which are supported on structures affixed to the machine servicing platform, such lifting apparatus usually being hydraulically operated.
In connection with wire-hanging systems, it is known in the prior art to utilize wire sections which are capable of being run out from the machine. Such systems include transversely extending support members located under the longitudinal beams of the wire frame, which supports are themselves supported on legs having rollers to facilitate their movement. In such wire changing systems, the entire inner structure of the wire loop can be displaced to a location beside the wire section with the exception of the cantilever-mounted traction and suction rolls. A track running transverse to the machine direction is utilized for transferring the new wire by means of a specially adapted wire carriage which comprises apparatus whereby the wire is spread out and opened over the wire pit with the aid of wire poles to thereby assume a configuration such that the inner structure of the wire loop, which has been displaced as described above, can be moved within the wire loop. The spreading of the new wire loop is accomplished in one or two manners, namely, by carrying the end bight of the wire towards the breast roll with the aid of wire pulls in which case the spreading means is fixed in the wire carriage, or by detaching the spreading means and moving it with the aid of a hoist. In a wire section provided with cantilever mounting, the transversely extending supports which carry the longitudinally extending beams of the inner structure of the wire loop are rigidly affixed to the foundation on the drive side of the paper machine. After dismantling certain elements of the paper machine and performing certain additional steps, the wire which has been dropped from the wire carriage will run to the side of the wire section and downwardly to be supported by the wire poles, can now be run into the machine to encircle the wire section. Although this conventional wire changing procedure is fast, it is disadvantageous in that the cantilever support members necessary for its operation are both heavy and expensive.